It is common practice to filter various kinds of liquids or fluids, such as blood, when the liquids are to be intravenously administered to a patient. Generally the liquid is passed through a filter housing containing a fibrous nonwoven bulk media sealed to the walls of the filter housing and supported by a grid or the like.
When dealing with blood filtration, because it is often days or weeks between obtaining a unit of blood and its preparation and infusion into a patient, a variety of blood-specific filtration problems can arise.
Typically, when blood is obtained from a donor to later be used for the purpose of transfusing a recipient, it often sits under refrigeration for several weeks and may develop gelatinous particulate precipitates or materials. Additionally, blood that is collected during surgery from surgical incisions or openings which is to be reinfused back into the patient can also develop gelatinous precipitates which need to be removed prior to the reinfusion of the blood.
The gelatinous materials and other agglomerates, such as fat agglomerates sometimes referred to as a "buffy coat", can range in size from less than 5 microns to up to several millimeters in diameter.
With specific regard to the removal of gelatinous particulate material from blood, the prior art has generally relied upon open-cell lattices such as open-cell foam which trap these gelatinous particulates through size exclusion. Such media suffer from easy blockage by the larger gels which spread out and occlude large areas of the media.
Pall U.S. Pat. No. 4,925,572, issued May 15, 1990, discloses a device for filtering blood products including a gel pre-filter for specifically removing gels present in whole blood samples. The gel pre-filter is formed of a non-woven web or "needled" web formed by passing plastic through a machine fitted with a large number of rapidly reciprocating, multiply barbed needles which randomly engage fibers and pull or push them through the thickness of the web causing the fibers from one face to be pulled to the opposite face where they may become entangled with fibers at that face. The Pall '572 reference discloses that as gel laden blood flows through the needled filter medium, small pores are randomly encountered, and they are sufficient in number to have the net effect of trapping or collecting all or nearly all of the gels within the medium.
Bentley U.S. Pat. No. 3,935,111, issued Jan. 27, 1976, discloses a filter device which removes fat agglomerates from blood utilizing an open-cell foam filter.
Both of the above referenced prior art devices teach the use of either a pre-filter or filter to remove gelatinous particulates from blood. However, because both of these devices remove the gelatinous particulate material either at or directly before the primary filter, these devices are prone to clogging and especially a blockage due to the retention and subsequent spreading out of large gels (a build-up of gelatinous particulate material) of the primary filter and hence the premature failure of the filter.
Therefore, it would be desirable to have a filter assembly which provides for the filtration of gelatinous particulate material from blood wherein the gelatinous particulate material removed does not distinctly reduce or inhibit the functioning of the filter device once it has been removed from the blood.